Agent: fix date handling — Costa Rica timezone and future cuotas

Two bugs from prod (server clock is UTC, user is UTC-6):

- get_recent_transactions returned future-dated Tasa Cero cuotas; it now
  excludes anything dated after the user's today, same rule as
  /transactions/recent.
- "¿Cuánto he gastado hoy?" answered for the wrong day: the prompt baked
  date.today() in at boot — frozen from startup AND in server-UTC (8 pm
  in Costa Rica is already tomorrow in UTC). The prompt no longer carries
  a date; a new get_current_date tool returns today in CR time plus the
  active billing cycle, and the prompt directs the model to call it for
  any relative date reference. today_cr() lives in timeutil (CR has no
  DST, fixed UTC-6).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/agent/agent.py

@@ -2,8 +2,6 @@
 
 from __future__ import annotations
 
-from datetime import date
-
 from agent_framework import Agent
 from agent_framework.openai import OpenAIChatCompletionClient
 
@@ -22,8 +20,10 @@ Context you can rely on:
   following month. When the user says "this month" or "last month" without
   qualifiers, assume they mean the calendar month unless they mention
   "cycle", "corte", or their credit card.
-- Today's date is {today}. Use it when the user says "this month", "last
-  month", "last year", etc.
+- You do NOT have a reliable clock, and the server runs in UTC while the
+  user lives in Costa Rica (UTC-6). Whenever the question involves a
+  relative date — "hoy", "ayer", "este mes", "este ciclo", "el año
+  pasado" — call get_current_date FIRST and derive ranges from its answer.
 - Amounts are stored as raw numbers in their native currency (see `currency`
   field on transactions/accounts). Tools that return `total_crc` are already
   converted; tools that return per-transaction amounts are NOT.
@@ -69,7 +69,10 @@ def build_agent() -> Agent:
     )
     return Agent(
         name="wealthysmart",
-        instructions=SYSTEM_PROMPT.replace("{today}", date.today().isoformat()),
+        # No date baked in: build_agent() runs once at startup, so anything
+        # substituted here freezes at boot (and in server-UTC). The model
+        # gets "today" from the get_current_date tool instead.
+        instructions=SYSTEM_PROMPT,
         client=client,
         tools=TOOLS,
     )

backend/app/agent/tools.py

@@ -13,7 +13,7 @@ write tool requires an explicit user-confirmation step in the UI.
 from __future__ import annotations
 
 import contextvars
-from datetime import datetime
+from datetime import datetime, time, timedelta
 from typing import Annotated, Optional
 
 from pydantic import Field
@@ -40,6 +40,7 @@ from app.services.budget_projection import (
     get_cycle_range,
 )
 from app.services import exchange_rate as fx
+from app.timeutil import today_cr
 from app.services.exchange_rate import (
     get_converted_amount_expr,
     get_current_rate,
@@ -140,7 +141,11 @@ def get_recent_transactions(
     q = select(Transaction).where(
         col(Transaction.transaction_type).notin_(
             [TransactionType.SALARY, TransactionType.DEPOSITO]
-        )
+        ),
+        # Tasa Cero generates future-dated cuotas; "recent" means already
+        # billed (same rule as /transactions/recent). Bound is end of the
+        # user's today, Costa Rica time.
+        Transaction.date < datetime.combine(today_cr() + timedelta(days=1), time.min),
     )
     if source:
         q = q.where(Transaction.source == TransactionSource(source))
@@ -491,7 +496,33 @@ def list_categories() -> list[dict]:
 
 
 # Registered with the agent in agent.py
+def get_current_date() -> dict:
+    """Today's date in the user's timezone (Costa Rica, UTC-6) and the
+    active credit-card billing cycle. ALWAYS call this before resolving any
+    relative date reference — 'hoy', 'ayer', 'este mes', 'este ciclo',
+    'el ciclo pasado' — the server clock and your own assumptions about
+    today are unreliable."""
+    today = today_cr()
+    # get_cycle_range(y, m) is the cycle STARTING on the 18th of m; before
+    # the 18th we are still in the cycle that started last month.
+    if today.day >= 18:
+        cycle_year, cycle_month = today.year, today.month
+    elif today.month == 1:
+        cycle_year, cycle_month = today.year - 1, 12
+    else:
+        cycle_year, cycle_month = today.year, today.month - 1
+    start, end = get_cycle_range(cycle_year, cycle_month)
+    return {
+        "date": today.isoformat(),
+        "weekday": today.strftime("%A"),
+        "cycle_year": cycle_year,
+        "cycle_month": cycle_month,
+        "cycle_range": [start.date().isoformat(), end.date().isoformat()],
+    }
+
+
 TOOLS = [
+    get_current_date,
     get_accounts,
     get_net_worth,
     get_recent_transactions,

backend/app/timeutil.py

@@ -1,4 +1,17 @@
-from datetime import datetime, timezone
+from datetime import date, datetime, timedelta, timezone
+
+# Costa Rica has no DST; a fixed offset is exact year-round.
+CR_TZ = timezone(timedelta(hours=-6))
+
+
+def today_cr() -> date:
+    """Current date in Costa Rica (UTC-6).
+
+    The server clock is UTC — at 6 pm in Costa Rica it is already "tomorrow"
+    in UTC. Anything user-facing that means "today" (agent answers, date
+    defaults) must come from here, never date.today().
+    """
+    return datetime.now(CR_TZ).date()
 
 
 def utcnow() -> datetime: